Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $37.30   11.861%   $41.7242   $41.72   $41.70   $41.70  
  Purchase #2 $61.34   12.181%   $68.8118   $68.81   $68.80   $68.80  
  Purchase #3 $10.35   10.222%   $11.408   $11.41   $11.40   $11.40  
  Purchase #4 $235.51   8.694%   $255.9852   $255.99   $256.00   $256.00  
  Purchase #5 $168.69   5.487%   $177.946   $177.95   $177.95   $177.90  
  Purchase #6 $14.92   7.628%   $16.0581   $16.06   $16.05   $16.10  
  Purchase #7 $185.97   12.333%   $208.9057   $208.91   $208.90   $208.90  
  7 purchase totals = $714.08       $780.8390   $780.85   $780.80   $780.80